How many electrons and ATP are required for the biological fixation...

The biological nitrogen fixation is catalyzed by the enzyme nitrogenase. The overall reaction for the reduction of one molecule of nitrogen (N_2$) to two molecules of ammonia (NH_3$) is given by:

$N_2 + 8e^- + 8H^+ + 16ATP \rightarrow 2NH_3 + H_2 + 16ADP + 16P_i$

From the balanced equation, the fixation of one molecule of nitrogen requires $8$ electrons and $16$ ATP molecules.

Answer: 8 and 16 respectively